This disclosure relates to wireless telecommunications. In particular, this disclosure relates to the resolution of a call contention condition after a wireless call is dropped.
Telecommunications systems have long dealt with the situation of “call collision” or “call contention” (formerly known as a “glare condition”). A call collision occurs when a telephone is attempting to establish an outbound telephone call, but before the outgoing call is established, an inbound call attempts to make contact with the same telephone. Telecommunications protocols generally specify how a call collision is handled. For example, the collision can be resolved by allowing the inbound call to take priority over the outbound call, or, alternatively, by allowing the outbound call to take priority over the inbound call. The call that does not have priority may be dropped.
In general, a call collision can occur when a first telephone attempts to call a second telephone at the same time as the second telephone attempts to call a third telephone. It is possible, though, for a call collision to occur with only two telephones, if the two telephones attempt to call one another at approximately the same time. This situation can be referred to as a symmetric call contention. In some telecommunications protocols inbound calls take precedence over outbound calls. The result in such protocols is that the outbound call associated with each telephone is dropped. Since both outbound calls are dropped, though, there is no longer any inbound call to be answered, and no connection will be made. The same problem arises if the telecommunications protocol gives precedence to outbound calls.
In some cellular telephone communication networks, symmetric call collision can result in both callers being routed to voicemail systems. When two callers attempt to call one another at approximately the same time, both callers are making use of the signaling channel. The network recognizes that the signaling channel is occupied, and it routes both calls to voicemail. This situation can arise when two parties are on a voice call with one another and their call is unintentionally disconnected. The unintentional disconnection of a call, called a “call drop,” can occur in a cellular telephone network as a result of a system problem, a cellular tower handoff problem, lack of channel availability, a dead spot in RF (radio frequency) coverage, or for other reasons. The two parties may then immediately and simultaneously attempt to call one another back, only to have the calls “collide.” Both of the callers are, frustratingly, routed to the voicemail of the person with whom they were just speaking.
The likelihood that two dropped callers will simultaneously attempt to re-establish contact is increased by the more widespread use of mobile stations (and even Caller-ID-enabled land line telephones) with an interactive “call log” that lists both incoming and outgoing telephone numbers. Without such a feature, the party who originally placed the call could typically activate a “redial” feature, while the party originally on the receiving end may not even know the caller's telephone number. If both callers have interactive call logs, though, it is easier for both to call one another at approximately the same time simply by selecting the newest entry in the call log.
U.S. Pat. No. 6,782,094 attempts to address the problem of two devices simultaneously attempting to call one another. It describes a system in which endpoints generally communicate over a primary network. In case of a failure in the primary network, the endpoints automatically attempt to communicate over a backup network. If a glare condition is detected in the backup network, each of the endpoints performs an algorithm to decide which endpoint is dominant. The non-dominant endpoint backs off and waits, while the dominant endpoint tries to reconnect. Each endpoint determines whether it is dominant by, for example, comparing its telephone number with that of the other endpoint, with the largest telephone number being dominant.
It has been recognized, though, as described in U.S. Pat. No. 5,056,083, that automatic resolution of call collision between human users can result in confusion and discomfort. A user generally expects, after dialing a party, to hear a ringback tone, followed by the voice of the party they have called. If two users are connected together, with each believing he has called the other, there will be a moment of confusion as the parties attempt to determine first, to whom they are speaking, and second, how it is that they came to be connected.
It would be desirable to mediate call collision events in a way that provides an improved user experience.